The present invention relates to a method for measuring the physical properties of a material.
The method according to the invention is particularly advantageous in measurement of the energy transfer characteristic and/or rebounding characteristic of an object.
More specifically, the method according to the invention can be advantageously utilized to determine the restitution coefficient of golf balls and the like.
In measurement of the energy transfer characteristic inherent to a material, a conventional method is known in which a viscoelasticity spectrometer is utilized to determine the energy transfer characteristic from energy loss caused by phase lag occurred when mechanical impulsive forces are applied to an object. However, this conventional method is accompanied by such a disadvantage that undesirable resonance will occur to hinder the exact measurement when more than 100 Hz of impulse frequencies are imparted to the object to be measured, and thus, an available upper limit of impulse frequencies usually remains at less than 100 Hz. In a particular case where more than 100 Hz is applied, a considerably expensive extra apparatus must be prepared to meet the requirement.
In measuring the physical properties of an object, several methods have heretofore been utilized in order to measure the rebounding characteristic or restitution coefficient of objects, such as golf balls. The simplest of these known methods is of man's actual performance of striking a ball. However, this method is naturally not too reliable in obtaining data because they depend on an individual's striking ability. Thus, another method which utilizes a striking machine in place of man's striking performance has been proposed, which is, however, disadvantageous in that the whole measuring system is quite expensive and not generally applicable.
Additionally, both of these known methods have another disadvantage in that various time consuming preliminary arrangements are required for effecting the measurng performance and obtaining data.
A further conventional method for measuring the restitution coefficient of golf balls is known in which a predetermined mass of projectile is shot against a sample golf ball by means of an air gun. However, this method also has a disadvantage that not only a large and expensive measuring system is inevitably required but also time consuming analysis are required before determining the restitution coefficient from the measured data.
As a matter of course, none of the above-discussed conventional methods are easily applicable to inspection of all of the products (golf balls) on the production line. In other words, the conventional methods are merely applicable to sampling inspection, from which, however, satisfactory inspection cannot be expected.